DARPA M3 Actuation

Project Objective

We seek to improve the energy efficiency of actuators used in robotic locomotion. We focus on analyzing the dynamics of human and bi-pedal robot walking gaits, and developing bio-inspired actuators and control methodologies that will deliver the required capacities. The improved efficiency will be demonstrated on a Cornell built bi-pedal robot and compared to traditional actuation.

Project Description

The rising need in robotic platforms that interact with human-made environments is driving forward the search for methods and technologies that will increase the current capacities and endurance of bi-pedal systems. Current robotic platforms have recently begun using bio-inspired designs and morphologies, to achieve this goal. The actuator technologies utilized with current systems are often inappropriate. These systems are usually not back drivable and continuously actuated by servo mechanisms throughout their motion, leading to horrendous inefficiencies and lack of robustness. The human bi-pedal walking gait requires continuously toggling the actuators between stall and some velocity, when implemented on a robotic platform. Using conventional electro mechanical servo-mechanisms, such as DC motors, puts the electro-mechanical power conversion far from the highest power conversion efficiency. Moreover, the proximity of the motors to the actuated joints increase the limb inertia and the actuation power as a result. Hydraulic actuators, on the other hand, separate the energy conversion mechanism (i.e. the pump) from the actuators, and thus minimize the actuation power overheads. Currently, hydraulics are also used inefficiently. Hydraulic systems use continuous power in robotics and do not utilize the ability to be back-driven. The high stiffness of the hydraulic medium is not well matched to the smooth motions, and compliance associated with biologically inspired platforms. Furthermore, the inbound fluidic energy from the negative mechanical power (Figure 1) is not recovered in the robotic systems to date, and vented out together with the excess energy generated by the pump. We propose not a single device or technology to improve the performance of robotic systems, but a holistic and innovative approach utilizing novel bio-inspired concepts and sound engineering principles to utilize and apply energy in new and efficient ways, recover energy when possible, and impedance matching the actuator/power system to the load and task required by application.

Figure 1: Mechanical power in a human walking gait. Winter, D., “Biomechanics and motor control of human movement,” Hoboken, N.J. John Wiley and Sons, 2009.